High-impact conservation: invasive mammal eradications from the islands of western Mexico

Aguirre-Muñoz, A., Croll, D. A., Donlan, C. J., Henry III, R. W., Hermosillo, M. A., Howald, G. R., ... & Samaniego-Herrera, A. (2008). High-impact conservation: invasive mammal eradications from the islands of western Mexico. AMBIO: A Journal of the Human Environment, 37(2), 101-107.

Islands harbor a disproportionate amount of the earth's biodiversity, but a significant portion has been lost due in large part to the impacts of invasive mammals. Fortunately, invasive mammals can be routinely removed from islands, providing a powerful tool to prevent extinctions and restore ecosystems. Given that invasive mammals are still present on more than 80% of the world's major islands groups and remain a premier threat to the earth's biodiversity, it is important to disseminate replicable, scaleable models to eradicate invasive mammals from islands. We report on a successful model from western México during the past decade. A collaborative effort between nongovernmental organizations, academic biologists, Mexican government agencies, and local individuals has resulted in major restoration efforts in three island archipelagos. Forty-two populations of invasive mammals have been eradicated from 26 islands. For a cost of USD 21 615 per colony and USD 49 370 per taxon, 201 seabird colonies and 88 endemic terrestrial taxa have been protected, respectively. These conservation successes are a result of an operational model with three main components: i) a tri-national collaboration that integrates research, prioritization, financing, public education, policy work, capacity building, conservation action, monitoring, and evaluation; ii) proactive and dedicated natural resource management agencies; and iii) effective partnerships with academic researchers in México and the United States. What is now needed is a detailed plan to eradicate invasive mammals from the remaining islands in the region that integrates the needed additional financing, capacity, technical advances, and policy issues. Island conservation in western México provides an effective approach that can be readily applied to other archipelagos where conservation efforts have been limited.

Little recovery of burrowing petrels after cat eradication

Cerfonteyn, M., & Ryan, P. G. 2016. Have burrowing petrels recovered on Marion Island two decades after cats were eradicated? Evidence from sub-Antarctic skua prey remains. Antarctic Science, 1-7.

In the 1980s, penguins dominated the prey remains of sub-Antarctic skuas Stercorarius antarcticus breeding on Marion Island, whereas on neighbouring Prince Edward Island burrowing petrels made up >95% of prey remains in nest middens. This difference resulted at least in part from the impact of introduced cats Felis catus on Marion Island’s burrowing petrel populations. Cats were introduced to Marion Island in 1949, and prior to their eradication in 1991, they killed an estimated 450 000 petrels each year, greatly reducing the densities of petrels breeding on the island. A repeat survey of skua prey remains showed that penguins still dominated the prey of breeding sub-Antarctic skuas on Marion Island in the summer of 2010–11, two decades after cats were eradicated from the island. The proportion of penguin remains decreased slightly compared to 1987–88, but this might be expected given the decreases in penguin numbers on Marion Island over this period. Regurgitated pellets confirmed the dominance of penguin prey on Marion Island. Taken together with the decrease in skua numbers on Marion Island over the last two decades, our results suggest that there has been little recovery in the population of at least summer-breeding burrowing petrels since cats were eradicated.

Recovery of seabirds to vertebrate management on Macquarie

Brothers, N. & Bone, C. (2008) The response of burrow-nesting petrels and other vulnerable bird species to vertebrate pest management and climate change on sub-Antarctic Macquarie Island. Papers and Proceedings of the Royal Society of Tasmania, 142, 123-148

Pest species management is causing rapid and significant changes to burrow-nesting petrel populations on sub-Antarctic Macquarie Island. The Weka, Gallirallus australis, was eliminated by 1989 and the Feral Cat, Felis catus, eradicated in 2000. The most abundant burrownesting petrel species currently, White-headed Petrels, Pterodroma lessonii, Antarctic Prions, Pachyptila desolata, and Sooty Shearwaters, Puffinus griseus, have yet to increase in numbers, but are expected to do so in the absence of cats. This study found evidence that Grey Petrels, Procellaria cinerea, began breeding again on the island in 1999, after an absence of over 100 years. Blue Petrels, Halobaena caerulea, and Fairy Prions, Pachyptila turtur, were found to be re-colonising Macquarie Island from offshore stacks after a similar absence. South Georgian Diving-Petrels, Pelecanoides georgicus, were also possibly recolonising the island. Despite the presence of Black Rats, Rattus rattus, most of the bird species discussed are considered capable of population increase. If European Rabbits, Oryctolagus cuniculus, are not eliminated or maintained in reduced numbers, some petrel populations will never fully recover. Climate change could have a negative impact on burrow-nesting petrels, and is likely to exacerbate the detrimental effects of the remaining pest species on vulnerable indigenous bird species, compounding the need for remedial action against rabbits in particular. Together with predictions that other petrel species will now return to breed, certain terrestrial bird species, alien to the region, may invade Macquarie Island as a consequence of the combination of pest eradication and changing climatic conditions.


More on Macquarie island cats

Fencing to eradicate several invasive predators in Hawai'i

Young, L. C., VanderWerf, E. A., Lohr, M. T., Miller, C. J., Titmus, A. J., Peters, D., & Wilson, L. (2013). Multi-species predator eradication within a predator-proof fence at Ka ‘ena Point, Hawai ‘i. Biological Invasions, 1-12.

Ka‘ena Point Natural Area Reserve on O‘ahu hosts one of the largest seabird colonies in the main Hawaiian Islands and supports three species of endangered plants. In order to stop chronic predation by invasive alien mammals on native species, a peninsula-style predator-proof fence was constructed around a 20-ha portion of the reserve in 2011. Multi-species predator removal efforts began upon fence completion; diphacinone poison in bait boxes spaced 25 m apart was used to remove black rats, house mice, and small Indian mongooses. House mice also were removed with multiple-catch live traps spaced 12.5 m apart. Feral cats were removed with padded leg-hold traps. Feral cats and mongooses were eradicated in 1 month, black rats were eradicated in 2.5 months, and house mice were eradicated in about 9 months. Since eradication, incursions of cats and mongoose have been rare (1/7.2 months), but incursion frequency has been higher for black rats (1/56 days) and house mice (1/36–47 days). Buffer predator control was conducted to limit predator access and prevent reinvasion around the fence ends along the shoreline. Even with the high initial fence cost and ongoing predator incursion management, this method is expected to become more cost effective than previous predator control efforts after 16 years. Record numbers of Wedge-tailed shearwaters and Laysan albatrosses have fledged from the reserve after predator eradication, and regeneration of native plants and invertebrates is being observed. With careful planning and persistence, predator fences can be a cost-effective method of protecting natural resources, and multiple species of predators can be eradicated with traps and first-generation anti-coagulents.

Breeding of Procellariidae before and after eradication of feral cats at Marion Island

Cooper, J. Marais, A.V.N., Bloomer, J.P. & Bester, M.N. 1995. A success story: breeding of burrowing petrels (Procellariidae) before and after eradication of feral cats Felis catus at sub-Antarctic Marion Island. Marine Ornithology 23: 33-37.

Greatwinged Petrels Pterodroma macroptera and Blue Petrels, Halobaena caerulea bred more successfully alter the eradication in 1991 of feral domestic cats Felis catus at subantarctic Marion Island. The larger Whitechinned Petrel Procellaria aequinoctialis did not show such improvement, although percentage burrow occupancy in the late breeding season increased significantly between 1982/83 and 1988/89 for that species, suggesting decreased cat predation during this period of cat control. Breeding success and burrow density of selected species of burrowing petrels should be monitored to ascertain the rate of recovery of their populations now that Marion Island is cat-free. 

Recovery of seabirds after cat control

Cooper J. & A. Fourie. 1991. Improved breeding success of great-winged petrels Pterodroma macroptera following control of feral cats Felis catus at subantarctic Marion Island. Bird Conservation International, 1:171-175.

A population of feral domestic cats Felis catus has existed at subantarctic Marion Island since 1951. From 1977 to 1990 an ongoing programme has utilized an introduced disease, shooting and gin-trapping in an endeavour to control cat numbers, with the eventual aim of their eradication. Burrowing petrels (Procellariidae) form the majority of the cats' diet. The breeding success of the winter-breeding Great-winged Petrel Pterodroma macroptera has varied between nil and 20.5% in the period from 1979 to 1984, due primarily to cat predation of chicks causing up to 100% mortality. In 1990, by which time cat numbers had been greatly reduced from their 1970s' peak, Great-winged Petrels had a breeding success of 59.6%, with chick mortality being zero. No signs of cat predation were observed. This finding provides good reason to continue the control programme until cats are finally eradicated from Marion Island.

Conservation of Zino petrel

Zino F. et al. (2001) Conservation of Zino's petrel Pterodroma madeira in the archipelago of Madeira. Oryx, 35, 128-136.

Birds restricted to islands are susceptible to extinction, and burrow or ground-nesting birds are particularly vulnerable to introduced mammalian predators. Human intervention has also played a vital part. Birds have been used as a source of food, and in more recent times the rarer species have suffered from specimen and egg collection. The island of Madeira and its resident species, which include the endemic Zino's petrel or Madeira freira Pterodroma madeira, are no exception. From subfossil evidence, this bird was once abundant. It was first recorded in 1903, and was already limited to the high central mountain massif of Madeira. By the middle of the century it was considered extinct, but a relict population was rediscovered in 1969. By 1985, all known breeding attempts were disrupted by introduced rats, to the extent that no young fledged. In 1986 the Freira Conservation Project was founded with the aim of increasing the population of Zino's petrel, by controlling rats and human interference, the principal perceived threats to the species. This control was extended to cats after the disaster of 1991, in which a cat(s) managed to get onto one of the breeding ledges and kill 10 adult birds. The results of these efforts have been positive and the small colony is making a slow, but steady recovery. To maintain this success, a conservation strategy for the future is suggested.

Seabird recovery after cat eradication on Ascension

Ratcliffe, N., Bell, M., Pelembe, T., Boyle, D., Benjamin, R., White, R., Godleya, B, Stevenson, J. & Sanders, S. (2010). The eradication of feral cats from Ascension Island and its subsequent recolonization by seabirds. Oryx, 44(1), 20.

The introduction of mammal predators to islands often results in rapid declines in the number and range of seabirds. On Ascension Island the introduction of cats in 1815 resulted in extirpation of large seabird colonies from the main island, with relict populations of most species persisting only in cat-inaccessible locations. We describe the eradication of feral cats from this large and populated island. The campaign had to minimize risk to humans and maintain domestic animals in a state that prevented them re-establishing a feral population. Feral cat numbers declined rapidly in response to the strategic deployment of poisoning and live trapping, and cats were eradicated from the island within 2 years. During the project 38% of domestic cats were killed accidentally, which caused public consternation; we make recommendations for reducing such problems in future eradications. Since the completion of the eradication campaign cat predation of adult seabirds has ceased and five seabird species have recolonized the mainland in small but increasing numbers.

Breeding success of seabirds at Ascension was low compared to that of conspecifics elsewhere, and the roles of food availability, inexperience of parent birds and black rat predation in causing this warrant further investigation. It is likely that the low breeding success will result in the rate of increase in seabird populations being slow.

Recovery of seabirds after the extirpation of cats

Hughes, B., Martin, G. R., & Reynolds, S. J. (2008). Cats and seabirds: effects of feral domestic cat Felis silvestris catus eradication on the population of sooty terns Onychoprion fuscata on Ascension Island, South Atlantic. Ibis,150(s1), 122-131.

The population of Sooty Terns Onychoprion fuscata breeding on Ascension Island in the Atlantic Ocean was monitored over 17 years (1990–2007). This period spanned the programme of feral Domestic Cat Felis silvestris catus eradication from the island, which commenced in 2001 with the last Cat recorded in 2004. We report on the abundance of Sooty Terns and Black Rats Rattus rattus before and after Cat eradication.

The Sooty Tern breeding population in the 1990s averaged 368 000 and Cats were killing Terns at an average rate of 33 adults per night. Following Cat eradication, adult Terns are no longer predated. However, egg predation by both Rats and Common Mynas Acridotheres tristis has continued with Mynas destroying more eggs than Rats. Unexpectedly, we observed a change in Rat predatory behaviour.
Following Cat eradication, Rats have become a major predator of Sooty Tern chicks. Despite this change, the Tern population has shown a season-on-season increase since Cat eradication, 48.8% in 2005, 8.2% in 2006 and 6.1% in 2007, and the breeding population increased to 420 000 birds in 2007. Incubation success improved from 66.0 to 84.4% during Cat eradication, before dropping down again to 67.9% after Cats were eradicated and Rat control measures were introduced. Index traplines were set for Rats and Rat numbers fluctuated widely immediately after Cats were eradicated but there were no significant differences that could be attributed to changes in Cat numbers. Ascension Island Sooty Terns breed every 9.6 months and juveniles defer breeding for seven seasons. Hence 2008 is the first year in which an increase in the breeding Sooty Tern population directly attributable to Cat eradication is likely to be detected. We conclude that long-term monitoring is essential to guide conservation practice even in this relatively simple predator–prey system.

Eradication of feral cats on a forested tropical island

Rodríguez C., Torres R. & Drummond H. (2006) Eradicating introduced mammals from a forested tropical island. Biological Conservation, 130, 98-105.

Methodologies developed in New Zealand for eradication of exotic mammals from temperate oceanic islands were adapted for use on a topographically complex, 194-ha, densely forested, tropical island off the Pacific coast of Mexico. Isla Isabel is a National Park and a nesting refuge for nine species of marine birds, but the island’s extraordinarily dense population of cats (113/k2) was annually killing 23–33% of nesting sooty terns.
We provide quantitative descriptions of the implementation and outcome of the methodologies over a period of three years, culminating in successful eradication of cats, but not rats. We also provide quantification of the effects of cat eradication on sooty tern mortality over a period of 11 years.

Eradication of feral cats leads to partial Seychelles magpie robin population recovery

Watson J., Warman C., Todd D. & Laboudallon V. (1992) The Seychelles magpie robin Copsychus sechellarum: ecology and conservation of an endangered species. Biological Conservation, 61, 93-106.

In 1977–1978 some 40 Seychelles magpie robins Copsychus sechellarum, the entire world population, survived on Frégate island. These lived in 12 territorial groups of up to six individuals. Their range on Frégate was limited by the amount of feeding habitat, specifically bare earth and leaf litter which occurred under mature shady woodland and in cultivated vegetable gardens. Two attempts were made to reintroduce the species to Aride Island in 1978 and 1979. These were unsuccessful and the translocations had to be abandoned when a new threat impinged on the parent population of Frégate in 1980.
By 1981 numbers there had declined to 18, with virtually no recruitment, and an increase in the feral cat population was implicated. A successful cat eradication programme by trapping and poisoning was carried out in 1981–1982. By 1983–1984 the population showed a recovery with recruitment again healthy, although the abandonment of agriculture on Frégate between 1979 and 1983 had caused a reduction in the amount of feeding habitat and in the carrying capacity of the island to around 25 individuals in eight territorial groups. A range of management options is discussed.

See also here.

Frigatebird returns to nest on Ascension for first time since Darwin

Endangered species may be saved from extinction after eradication of feral cats that had been eating its chicks
Robin McKie, science editor The Observer Saturday 8th December

One of the world's rarest seabirds has returned to remote Ascension Island in the Atlantic 150 years after its colony was wiped out by feral cats. Last week ornithologists spotted two nests containing eggs being guarded by Ascension frigatebirds, the first of the species to breed there since Charles Darwin visited the island in the early 19th century.

Ascension frigatebirds only survived in a small colony on a nearby rocky outcrop where they were considered to be highly vulnerable to outbreaks of disease and oil spills. But now they have returned to the island after which they are named, raising hopes that the vulnerable bird may be rescued from extinction.

The news marks the success of a project which has cost UK taxpayers more than £500,000 and has involved the eradication of hundreds of feral cats that had been eating frigatebird chicks.

"We are absolutely overwhelmed," said Derren Fox, a conservation officer based on Ascension. "We thought it would take decades for the Ascension frigate to come back and breed after we had got rid of the island's feral cats. But we have already succeeded after only a few years. This suggests we have a real chance of saving the Ascension frigate."

The project's success also raises hopes of saving colonies of other species threatened by feral animals. These include populations of seabirds and amphibians on Montserrat, Gough Island and South Georgia, which are all ravaged by rats, mice and other wild creatures.

In the early 19th century, Ascension Island was home to more than 20 million seabirds, mainly masked boobies, black noddies, brown noddies and Ascension frigatebirds. The frigatebird was considered to be the most important because it was unique to the island. Adults are about 30 inches in length while males have distinctive red sacs on their chests which they inflate during courtship.

Around 1800, rats – accidently introduced by settlers – began to kill off chicks. Cats were imported to kill the rats but instead joined in the killing of frigatebird chicks. "By the time Darwin visited the island in 1836, there were only a few frigatebirds left and the last few were killed off not long after he left," said Clare Stringer of the RSPB, which has played a key role in re-establishing the bird on Ascension. Only a small colony of around 10,000 survived on Boatswain Bird Island, a rocky outcrop off Ascension's east coast which could not be reached by cats.

In 2002, the RSPB – backed with funding from the Foreign Office – launched a programme to eradicate Ascension's feral cats. "It was slightly tricky," said Stringer. "We had to avoid killing islanders' pet cats and kill only feral animals. Owners were told to collar and microchip their pets. Then traps were laid and feral cats caught in these were put down."

In 2006, Ascension was declared to be free of wild cats. "It has taken six years to get frigatebirds to start to recolonise the island since we got rid of the feral cats and frankly it could have taken much longer," said Fox, who – with fellow conservation officer Stedson Stroud – has been monitoring the island for signs of the frigatebird's return. "We now have two nests being tended by parent birds and that should encourage a lot more to settle here in future."

http://www.guardian.co.uk/environment/2012/dec/08/frigatebird-returns-to-ascension